Title from PDF of title page (University of Missouri--Columbia, viewed on Feb 19, 2010). The entire thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file; a non-technical public abstract appears in the public.pdf file. Thesis advisor: Dr. John D. Robertson. Includes bibliographical references.

Risk assessment of trace-metal contamination in soils requires predictive models that can accurately describe the complex uptake processes at the soil-plant interface, which are usually characterized by the coexistence of and interaction between multiple components. Competing cations such as Ca and H can affect metal availability to plants and subsequent rhizotoxicity. The biotic ligand model (BLM) has been proposed as a promising approach to model these interactive processes. Under the BLM assumption, we designed experiments to investigate how the solution chemistry is correlated with metal uptake and rhizotoxicity. Our first goal is to acquire a set of BLM parameters that can accurately represent the experimental data over varied solution conditions and parameters that are easy to integrate with general speciation models. The second objective is to get insight into the physical nature of the interactions. Our titration experiments revealed three types of biotic ligands in the pea roots with defined site densities and stability constants with H. Our ion sorption experiments estimated the surface-adsorption stability constants of Ca, Mg, Cd, Cu, Ni, and Zn with excised fresh pea roots. Our 48-h root growth tests have established the formation constants (KMe's) of living pea roots with Ca, Cd, Cu, Ni, and Zn. In these studies, we hypothesized and confirmed that the concentration of the metal-root complexes correlated with observed rhizotoxicity and that Ca, H, and trace metals competed for root absorption where lower solution pH decreased both Ca and metal uptake. Root elongation was found to be highly sensitive to root Ca content rather than merely to the direct toxic effects of the trace metals. It is shown that the physiological complexity arising from a living root affected our modeling so that adjustable KMe values, as a function of solution and root chemistry, are required for good model fits. The established model parameters were tested in hydroponic mixture solutions for their ability to predict the uptake of multiple metals simultaneously. The joint effects of Cd, Cu, and Ni in mixtures on root growth were studied and the potential interactions between these ions were also investigated.

There are two main components to the research: the theoretical and the experimental. Chapter 2 contains an analysis of the state of soil quality guidelines and the scientific methods used to determine them. A number of recommendations to improve soil quality criteria for trace metals are offered including the importance of considering bioavailability and the need to use realistic conditions, trace metal sources and organisms. / A critical review of the literature dealing with predicting the availability of trace metals to plants is presented in Chapter 3. We found little agreement among hundreds of similar studies which relate plant metal uptake to the amount of metal extracted by selective chemical dissolution procedures. An extensive summary of the data shows clearly that the extraction methods are not widely applicable. Differences between individual soils, their metal retention capacities, as well as plant factors and environmental conditions contribute to the variability of the results. Alternative ways of assessing bioavailability are suggested. / The experimental component of the thesis focuses on the availability of trace metals to plants. In Chapter 4 the uptake of Cu from different soil pools was examined and the free metal ion (Cu2+) was found to be the best predictor of uptake by lettuce (Latuca sativa cv. Buttercrunch), ryegrass (Lolium perenne cv. Barmultra) and radish (Raphanus sativus cv. Cherry Belle). / In Chapters 5 and 6 we examined the effect of low-cost in-situ treatments on the availability of metals to plants in greenhouse and field experiments. Synthetic zeolites, P amendments, organic matter and clean soil were used and their effect on the bioavailability of Cd, Cu, Pb, Ni and Zn evaluated. The plants for the experimental work were lettuce and perennial ryegrass. Only the clean soil treatment was consistently effective in reducing the concentration of metals in the plant. We also wanted to determine whether the trace metals in the plant tissue came from the soil or from direct deposition of pollutants on the leaf surfaces. We found little evidence that metals in plants were a result of atmospheric fallout. / A method for the accurate analysis of total metal concentrations in a range of contaminated soils including those containing oil and grease was developed (Chapter 7). For this research the trace metals of concern are Cd, Cu, Ni, Pb and Zn---all commonly found in urban/industrial soils. The proposed method using HNO3/HClO4 has several advantages over the common HNO3/H2O2 procedure. We were able to digest larger soil samples and hence the final concentration of trace metals was usually in the range for analysis by inductively coupled plasma atomic absorption spectrometry or flame atomic absorption spectrometry.

Soil quality guidelines are currently based on total trace metal loads. There is a need to define indices of bioavailability to allow reasonable predictions for plant metal uptake and toxicity in soils. Trace metal toxicities to plants often correlate best with free metal ion activities. The first objective was to develop a plant bioassay that is sensitive to trace metals at concentrations realistic for soils. The root elongation of lettuce Lactuca sativa 'Buttercrunch' was used as toxicological endpoint. This endpoint was sensitive and reproducible to environmentally relevant concentrations of Cd, Cu, Ni, Pb and Zn. The second objective was to test whether free metal ion activities are constant predictors of metal toxicities in synthetic solutions and in soil extracts that differ in their concentrations of cations and ligands. The root elongation assay was used to test this hypothesis. In synthetic solutions, the rhizotoxicity of Cd, Cu, Ni, Pb and Zn decreased with increasing Ca and H concentrations. This could not be explained with the effect of higher cationic concentrations on root growth or on solution speciation. It was concluded that Ca and H inhibited the rhizotoxicity of all metals tested. The rhizotoxicity of Cu and Cd was further examined in soil extracts. Both metals became less rhizotoxic at higher H and dissolved organic matter concentrations. The rhizotoxicity endpoints from the experiments in synthetic solution were used to develop parameters for a Biotic Ligand Model (BLM) for Cd, Cu, Ni, Pb and Zn. The BLM accounts for solution speciation and interprets cationic inhibition of rhizotoxicity as competition of metals with Ca and H for potential sites of rhizotoxicity. The BLM predicted metal rhizotoxicity better than the free metal ion activity in synthetic solutions and in soil extracts. Different models were tested against literature rhizotoxicity data for metals at different Ca and H concentrations. Predictions for metal rhizotoxicity given by BLM, Gouy-Chapman-Stern model and Freundlich equation model were compared with predictions based on free metal ion activities in solution. The BLM predicted rhizotoxicity most accurately. The BLM seems promising for predictions of metal toxicity and metal bioavailability in soils to support site-specific environmental risk assessments.

Thesis (M.S. - Hydrology)--University of Arizona, 1984. / Includes bibliographical references (leaves 68-72).

Thesis (M. Sc.)--University of Hong Kong, 1993.

Thesis (M. Sc.)--University of Hong Kong, 1993.

Thesis (M.Sc.)--Memorial University of Newfoundland, 2001. / Includes bibliographical references.

Magister Scientiae - MSc / The current study investigated application of natural adsorbents in brine treatment. Brines are hypersaline waters generated in power stations and mining industries rich in Mg2+, K+, Ca2+, Na+, SO4 2- , Cl- and traces of heavy metals, thus there is a need for these brines to be treated to recover potable water and remove problematic elements. Natural adsorbents have been successfully used in waste water treatment because of their high surface area and high adsorptive properties when they are conditioned with acid or base. The investigation of pH showed that natural adsorbents did not perform well at low pH of 4 and 6. The adsorbents were able to work efficiently at the natural pH of 8.52 of the brine solution. These results show that natural adsorbents hold great potential to remove cationic major components and selected heavy metal species from industrial brine waste water. Heterogeneity of natural adsorbents samples, even when they have the same origin, could be a problem when wastewater treatment systems utilizing natural clinoptilolite and bentonite are planned to be developed. Therefore, it is very important to characterize the reserves fully in order to make them attractive in developing treatment technologies. / South Africa

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